Generally speaking, a grindstone is usually used to sharpen the blades of tools such as a kitchen knife, a fruit knife and knives for other purposes once these knives become blunt. By means of applying the blade of a tool reciprocally on a grindstone, the blade will recover its sharpness. However, besides time and energy consuming, a considerable skill will also be needed to achieve an excellent blade sharpening effect. Otherwise, all one can do is to assign the sharpening work to a tool shop which specialized in the job. Besides the reason that the quality of grinding cannot be easily controlled when it is processed manually, the forementioned defects are also caused by the unavailability of of an electrical tool grinder which is featured for its portability, suitability for household use, energy-saving and rapidity.
In spite of the availability of such similar inventions as those disclosed under U.S. Pat. No. 3,258,878, U.S. Pat. No. 3,800,480, U.S. Pat. No. 2,775,075, U.S. Pat. No. 2,865,141, U.S. Pat. No. 2,860,452, U.S. Pat. No. 4,333,273 and U.K. Patent No. 2,123,323, but viewing from their structures, it can be seen that grinding wheels are being used for the sharpening of tools. Upon grinding, the edge surface of the grinding wheel will keep in contact with the blade of a knife for the grinding process. Due to the fact that it is made of a very hard steel, it can conduct a strong grinding against any tool which is being processed (especially effective against a tool made of steel or any tool which has no blade). However, the following defects can also be easily made:
1. When the hard grinding wheel is pressing against a tool, its hardness contact will produce an extremely strong counter-active force, which makes the tool unable to be held steadily, and thus will easily produce a jumping phenomenon, and will further cause intermittent contacts between the grinding wheel and the tool i.e. the grinding process of the tool will be conducted in an intermittent manner. In this way, the contacting angle and the depth between the blade and the grinding wheel will not be kept consistently. Therefore, the blade which is thus processed will not be even and smooth. That is to say, after grinding the sharpness of the blade is usually unsatisfactory. PA1 2. As the surface of a grinding wheel is rather rough, the iron filings which is produced at the time of grinding will easily be adhered onto the surface of the grinding wheel. Such iron filings makes cleaning impossible. In addition, both the grinding wheel and the tool are of a hard nature. It makes wearing easy for the grinding wheel, which will have to be replaced frequently. However, as the installing of a grinding wheel is quite complicated, that makes replacement uneasy, and the expenses involved will also be very high.
In view of the above defects, with his years of experience in the manufacturing of knife tools, the inventor made up his mind to conduct an active continuous study and research in the said field. After repeated experiments and improvements, he managed to complete a knife-grinder for household use as disclosed under the present invention. And its main object lies in diminishing the size of the knife grinder to enable it be gifted with the features of easy portability and operation, with two grinding wheels which are facing one another and extending slighly outward and having an appropriate angle of elevation being driven by a motor to enable the two grinding wheels for easy replacement when necessary; and also enable two opening grooves to be set outside the grinding wheel and fixed onto the upper cover of the machine body by facing each other at the interior lateral side of the two grinding wheels to form a knife stand, so that a knife can be inserted into either one of the opening grooves according to the shape of the two lateral blades of the tool, to the ultimate effect of allowing it to be operated by everybody, rapidly processed, convenient and energy-saving.